Phonon and free-charge-carrier properties ofZn1−xMnxSeepilayers grown by molecular-beam epitaxy

Abstract

Far infrared and mid infrared ͑FIR-MIR͒ reflectivity measurements have been carried out on two different series of undoped and chlorine-doped Zn 1−x Mn x Se epilayers grown by molecular-beam epitaxy. The FIR reflection studies performed upon the series of undoped Zn 1−x Mn x Se samples suggest an intermediate-mode behavior for the optical phonon modes in the composition range ͑0 ഛ x ഛ 0.43͒. In addition to the known ZnSe-like and MnSe-like phonon resonances a "weak-mode" feature is found below the MnSe-like phonon band. The frequency of this feature shows a temperature and Mn dependent redshift. We suggest that this feature originates from the alloy disorder present in the samples. The shape of the reststrahlen band is found to change significantly with layer thickness. This is discussed in some detail for pure ZnSe epilayers. To extract some information about the electron effective mass, we performed room-temperature plasma edge measurements on chlorine-doped n-type Zn 1−x Mn x Se epilayers ͑0 ഛ x ഛ 0.13͒. Via Drude-Lorentz-type multioscillator fits to our data, we extracted the optical electron effective mass ͑m op * ͒ in a series of doped Zn͑Mn͒Se:Cl samples with different Mn contents and free-electron concentrations. Our results indicate that m op * in Zn 1−x Mn x Se is lower than that for ZnSe. In n-type chlorine-doped ZnSe samples with different free-electron concentrations, m op * varied from 0.133 m 0 to 0.152 m 0 , while in Zn 0.87 Mn 0.13 Se: Cl samples, we found a variation from 0.095 m 0 to 0.115 m 0 within about ±9% experimental accuracy. From theoretical calculations, we determined the extrapolated room-temperature band-edge electron mass in ZnSe and Zn 0.87 Mn 0.13 Se to be about 0.132 m 0 and 0.093 m 0 , respectively. Additionally, from electrical Hall effect measurements on Zn 1−x Mn x Se: Cl epilayers, we found a drastic reduction in the free-electron concentration with increasing Mn content. The incorporation of Mn increases the resistivity and decreases the mobility of the free charge carriers in the samples.

Large positive magnetoresistance effects in the dilute magnetic semiconductor (Zn,Mn)Se in the regime of electron hopping

“…The layer structure consists of an undoped ZnSe buffer followed by the n-type Zn 1Àx Mn x Se:Cl layer with a thickness of about 1 lm. 17,18 Mn atoms are isovalently substituted for Zn atoms. The Cl donors occupy Se sites.…”

Scaling approach to hopping magnetoresistivity in dilute magnetic semiconductors

“…25,26 The transport measurements were performed in van-der-Pauw geometry. In band can be neglected and the conductivity is due to hopping of electrons via donor impurities.…”

Crystal coherence length effects on the infrared optical response of MgO thin films

“…21 It is worth noting that this suggests that even the high crystalline quality of the IBAD film is not sufficient for a bulk damping constant; substantial film thickness and lateral dimensions of high crystalline quality may be necessary to obtain a sharp resonance and subsequent high-reflectivity characteristic of the single crystalline Reststrahlen response, as has been demonstrated in other thin film systems. 22 This may have implications on the feature size in both thickness and lateral dimensions for devices designed around the Reststrahlen response.…”